That Type Ia SN have a typical luminosity of 1043 ers/s, which we learned from figuring out how to measure distances to nearby galaxies that happened to host Type Ia Sn in the past, using a list of facts that is much longer than this one.

That, in the absence of dust, the peak luminosity of Type Ia SN correlates with the color of the supernova and the rate at which it fades.

That dust causes reddening and dimming of light, but in a usually predictable way which depends on wavelength.

That the unreddened, undimmed color and luminosity of a distant, redshifted supernova can be estimated from the data alone.

That the peak luminosities of Type Ia SN at different redshifts can be compared, even though observations measure different parts of the spectrum due to the cosmological redshift.

As long as this list is, it’s still highly incomplete, and takes for granted that we know even more basic things like “how do I calibrate how many ergs/s are coming from an astronomical object that I detect as a fuzzy blotch in my CCD detector?”. It represents decades of efforts by many hundreds of people (many of them theorists, but theorists working on Stuff That Exists), most of whom didn’t think twice about the existence of dark energy.

Given the above, one possible physics-biased reading of Simon’s article is that if you limit astronomers’ ability to go forth and characterize what the universe is actually like, no one will be laying the foundations for the next generation of crazy-physics-you-can-study-in-space. For astrophysics, the Universe is our LHC, and we’ve got to be free to characterize our widgets, even if they’re boring ole brown dwarfs rather than panels of supercooled silicon wafers.

Now, all of this diatribe is not meant to minimize the role of outside the box theory. You absolutely need that too. However, it’s not the only necessary thing, and it’s not for everyone. There’s an old chestnut that theorists are judged by their best paper and observers/experimentalists by their worst. In other words, once Alan Guth came up with inflation, he was rightly marked as a superstar, and he can safely spend the next three decades writing papers on Romulan cloaking devices if he chooses. However, if an experimentalist writes a paper saying they’ve detected Romulan cloaking devices, no one is going to believe them when they later say they’ve discovered the Higgs. Tempermentally, most people are probably more suited to one camp than the other. I know that I have a pragmatic streak a mile wide, and thus I’m better off in the “stuff that exists” camp. I can understand why that sounds terribly dull to Sean, but I’d bet he’s glad me and my ilk are doing so.

Quite Julianne.
And can one know for sure what does or does not exist?
Who in Europe or Asia would have believed there was a continent called America, before the first ships returned. Of course those who lived on the continent new it ‘existed’. And yet all those guys who later went searching for the mythical El Dorado, never found gold – ahhh gold, the gold rush, gold feever…

PS how does one know if the aliens have a cloaking device or not. I hear Baghdad didn’t know what hit them. They were radio ‘blind’
Invert with paint to see something that doesn’t exist better

SEAN

DUDE WTF MY NAME IS SEAN

a cornellian

I’m with Julianne. (Only more so as I am likely going in to soft condensed matter)

http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

It’s possible that my personal judgment about what qualifies as “perfectly obvious, and therefore possible to joke about” is different than other people’s. So even if people do get the joke, let me be serious for a moment.

I think it’s perfectly obvious that a healthy scientific enterprise will spend a large majority of its effort working on things that definitely exist and trying to understand them better. I think it’s perfectly obvious that we can know the basic features of something and still have lots of fascinating stuff to learn about its detailed workings. I think it’s perfectly obvious that the vast majority of interesting physics has nothing (or little) to do with uncovering the fundamental laws of nature. And I think it’s perfectly obvious that outside-the-box theory is not for everyone.

And I also think that I shouldn’t have to append such a disclaimer every time I express excitement or interest in some bit of esoteric theory. An expression of interest in subject A should not automatically be read as an expression of disrespect for subject B. The number of times I have read “my particular bit of relatively-down-to-earth science is really interesting, even though it’s not high-falutin’ theory, dammit!” is considerably larger than the number of times I have read “only high-falutin’ theory is interesting.” There certainly are misguided souls who think in this latter way, but unless I am laboring under a dramatic systematic error, they are vastly outnumbered by the people who are complaining about their existence.

One of the reasons I wrote about the preferred direction in inflation is that it’s a much more representative example of theoretical cosmology than Boltzmann’s Brains or some of the other esoteric speculation we like to wallow in. It was a straightforward extension of standard inflation, involving lots of honest calculation with spherical harmonics, culminating in a set of predictions that could be directly compared with existing data. It goes without saying (I would have thought) that the whole enterprise would be completely pointless without the hard work of understanding the plasma physics behind the CMB and going out and collecting all of those radio waves.

instigator

This is like a reality show. On the next Cosmic Variance, Mark gets drunk and ends up in the jacuzzi, while Sean and JoAnne force Risa to choose sides! Baaa na na na, ba da da bum ba da da! (That was the theme song.)

http://blogs.discovermagazine.com/cosmicvariance/julianne Julianne

And I also think that I shouldn’t have to append such a disclaimer every time I express excitement or interest in some bit of esoteric theory. An expression of interest in subject A should not automatically be read as an expression of disrespect for subject B.

Exactly right. I hope that people know that some of the back and forth on CV is goodnatured joking among people who like and respect each other. But, a link to the previous baryon post made me a bit concerned that some people might easily have gotten an incomplete picture about how I view theory, and not realize that just because it’s not my style, that I don’t think it’s a fabulous thing to be doing. At the same time, I had some lingering thoughts about Simon’s article which I wanted to get out there, trying to explain why some nitty gritty classical astronomy is relevant to what the physicist readership spends its time thinking about.

So CV readers, be assured I think Sean is a dude. At least until I know what happens after the hot tub episode.

http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

You know perfectly well what happened, we’re just bound to secrecy by the network’s contract, or at least until the episode airs. All I’m saying is, from now on I’m keeping Daniel away from the tequila.

Sam Gralla

Awesome posts, Julianne. I love the sense of humor. Poor Guth…

tyler

I love this kind of back & forth, and yes, it’s pretty obvious that you’re not really mad at each other.

It seems clear from the outside that the two approaches are necessarily complimentary. Rigorous observation and experimentation in “known” areas is needed to uncover those exceptions which point out an incomplete or incorrect currently accepted theory, which then must be replaced or extended via “out of the box” conceptual theorizing…which eventually leads, hopefully, to some new form of “known” or accepted theory. Lather, rinse, repeat.

Bill C

Just to add an particle experimentalist’s spin to the discussion… Most experimental papers are broadly classifiable as either searches or measurements. The searches, in turn, could be either well-motivated (many famous theorist wrote lots of papers predicting it) or simply turning over rocks to see what crawls out. Physics advances (or can advance) by both and neither is inherently more valuable a priori. We need both measurement and search. You can go for your Nobel with the high-risk, high-reward “search-only” strategy but we know for sure that improving the W mass measurement by a factor of two or three will teach us a LOT.

Personally, I find that I tend to alternate between searches and measurements.

smm

There’s an old chestnut that theorists are judged by their best paper and observers/experimentalists by their worst.

nice. i think the truth behind this saying is at the heart of physics (science): it’s more important to bring our thinking in line with careful observations and experiments, rather than the other way around. i’m sure i’ll get a lot of milage out of it!

brad

It’s also not so much about some abstract concept of “worth” as it is how people derive
satisfaction from what they do. As a theorist who works on “stuff that actually exists”, I
derive my personal rewards from seeing how scribblings on the page (or screen) actually
translate into real, observable photon-generating events gazillions of miles away. I am
willing to admit to the sheer coolness of early universe particle physics and whatnot, but
I believe I would find it unfulfilling to have spent twenty years writing papers and not know if
any of them were realised in nature or not.

On the other hand, there is the one in a million shot that deep ponderings will fundamentally
change our view of nature. I imagine thats what drives the esotericists. I suppose it depends
on whether you’re swinging for the fences, or hitting for average…

Ellipsis

Relax and just let theorists do their thing. Everything will work out in the end.

(Note that experimentalists/observers on average get slightly higher salaries, have more tenured faculty positions [ahem…!], and get more Nobel prizes on average than theorists, so absolutely no reason to mope — personally I feel extremely lucky to be in the “pragmatic experimentalist” camp.)

Jeff Harvey

The real question is whether Sean’s Poker playing would improve
if he spent more time working on things that definitely exist.

http://www.twistedphysics.typepad.com Jennifer Ouellette

Ooh! Jeff’s trolling for a smackdown! And all because he kicked our butts at Poker Friday night…

http://blogs.discovermagazine.com/cosmicvariance/julianne Julianne

Poor Guth…

I meant to be affectionate. He was one of the best instructors I ever had at MIT, and I wouldn’t say a word against him. Absolutely every word and concept that came out his mouth was crystal clear and perfectly explained. Plus, he came across as a genuinely nice guy.

http://quantumnonsense.blogspot.com/ Qubit

The more you think about something that exists; the more it seems like it is not real! The more you think about something that does not exist; the more it seems real!

The closer you get to the Theory Of Everything, the closer you get to not being real. The further you get from a TOE, the closer you are to being real! The TOE is not real or imaginary; it’s the real Theory Of Everything that’s imaginary!

It really does not matter what I think about or read about, I simply cannot say whether I exist or not. It seems to me that the reason I am here; is because everybody else exists, but that does not mean I am real or still alive (Watch V for Vendetta). I just have to have the imaginary potential to collapse everybody else’s imaginary potential so I can be observed as real, even if I have never been born! Failing that; I just have to have the potential to observe an object that can have more potential than any Theory Of Everything, then slide down the hill on the other side. Black Holes and dark matter are boring and governed by relativity, “Nonsense is where it’s at now!”

Qubit

http://mingus.as.arizona.edu/~bjw/ Ben

There’s an old cliche that nobody believes a theorist’s result except the theorist himself, and everybody believes an experimenter’s (or observer’s) result except the experimenter herself.

Old cliches, of course, get to be old cliches by being true.

fh

Heck for most people I talk to it is the other way around. We studied physics because we were curious about how the world works and now we find ourselves doing calculations that have almost certainly no, or at best a tenuous connection to reality.

http://knotmyline.wordpress.com/ Ron Hager

How can we be sure that Sean or maybe even Quasar9 himself is not one of the aliens and is using this fabulous cloaking device on us?

Myhatma Gander

“Plus, he came across as a genuinely nice guy.”

He is indeed. Proof: even the people who see him sleeping in their seminars like him.

Michael Wood-Vasey

While I completely agree with your list and point that many, many things have been done to bring us where we are today in our lack of understanding of dark energy, as a very minor technical note, I wish to mention just a bit regarding the following two remarks quoted below:

“””
That Type Ia SN have a typical luminosity of 10^43 ers/s, which we learned from figuring out how to measure distances to nearby galaxies that happened to host Type Ia Sn in the past, using a list of facts that is much longer than this one.
“””

It was important to learn that Type Ia SN had a typical luminosity, but not what its value was, to discover the accelerating Universe. Doing this was certainly aided by other known distance indicators, although after the fact SNe Ia alone can tell you that they are standard(izable) candles. It was not important to know what the luminosity was in erg/s. Speaking of which,

“””
takes for granted that we know even more basic things like “how do I calibrate how many ergs/s are coming from an astronomical object that I detect as a fuzzy blotch in my CCD detector?”.
“””

As observers, we don’t really actually have a good answer to this question. I can tell you how many erg/s are hitting my detector rather well. However, relating that to how many erg/s were actually emitted by the astronomical object in the given area subtended by our aperture is a far more challenging problem. Our ability to make relative measurements is far, far greater than our ability to make absolute measurements. While we’re discussing basic research things that should be done in astronomy, this is one of the very important things that we should probably figure out how to do well. And at the present moment it is in fact future planned dark energy missions/experiments that are most driving this need for basic improvement in how we do astronomy.

http://backreaction.blogspot.com/ B

The ‘Why’ and the ‘How’ are both good questions that one should ask. One just shouldn’t mix them up too much. If I’d ask myself why do I exist and why is now ‘now’ and not ‘then’ I’d never finish any paper. So I export these question to my blog Best,

B.

http://blogs.discovermagazine.com/cosmicvariance/julianne Julianne

It was important to learn that Type Ia SN had a typical luminosity, but not what its value was, to discover the accelerating Universe.

However, the value is important if you’re going to decide that they might be detectable at z=1. Maybe you don’t need to know more than a significant digit or two, but it’s not unnecessary information. Moreover, the good relative distances were critical for nailing down the time-delay/color/luminosity relation.

You’re certainly right that absolute photometry is still in the dark ages. I know of various astronomers who’ve been working on it/griping about it for a while (Stubbs, Hogg, and a woman-who’s-poster-I-saw-at-the-AAS-but-I’m-blanking-on-the-name who had actually proposed a satellite to nail it down). It will definitely be a bonus if the dark energy fervor has the byproduct of nailing this down.

Ellipsis

a woman-who’s-poster-I-saw-at-the-AAS-but-I’m-blanking-on-the-name who had actually proposed a satellite to nail it down

That would be (my friend and colleague) Susana Deustua, along with colleagues of hers. See http://www.starcal.org. There are several smaller projects that may get us a fraction of the way there in the meantime. STARCaL has other uses (in climate studies, etc.) as well.

http://blogs.discovermagazine.com/cosmicvariance/julianne Julianne

That’s her! Thanks for the name! She was very interesting to talk with, but unfortunately I have a mind like a steel seive, and I don’t have my notes about who I talked with on me at the moment.